Chuck Rolke created PROTON-1523:
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Summary: [proton c] API unclear how incoming_capacity and
max_frame work
Key: PROTON-1523
URL: https://issues.apache.org/jira/browse/PROTON-1523
Project: Qpid Proton
Issue Type: Bug
Components: proton-c
Affects Versions: 0.17.0
Reporter: Chuck Rolke
Two settings are available to throttle incoming traffic. These operate in units
of bytes:
* pn_transport_set_max_frame
* pn_session_set_incoming_capacity
Suppose a user sets a max_frame to 1 Mbyte and incoming_capacity to 2 Mbytes.
How many 200-byte hello-world messages might a user expect to be able to
receive before the local incoming-window closes? 10,000? The answer turns out
to be 2.
The logical disconnect is that the user interface incoming_capacity operates in
bytes but the AMQP protocol over the wire operates with an Incoming-Window in
frames. In the user's case the API assumes full frames and sets
Incoming-Window = (incoming_capacity / max_frame), or 2. When the sending peer
sends 200-byte messages the actual incoming capacity is 400 bytes and not
2Mbytes.
The rules (AFAICT) are:
{noformat}
IF (max_size is specified)
incoming_window = incoming_capacity / max_size
ELSE
incoming_window = 2147473647
ENDIF
{noformat}
Noting:
* Incoming capacity is achieved only if the peer sends max_size frames.
* If max_frame is not set then the incoming_capacity setting is ignored.
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